Dear visitor, welcome to SPRINKLER TALK FORUM - You Got Questions, We've Got Answers. If this is your first visit here, please read the Help. It explains how this page works. You must be registered before you can use all the page's features. Please use the registration form, to register here or read more information about the registration process. If you are already registered, please login here.

Installing Sprinklers with 1" Female NPT Inlet

Iam installing a few Rainbird Falcon 6504 sprinke heads to irrigate a large area. These come with 1" female NPT inlets (most other sprinkler heads come with 3/4" inlets). Can I use the regular 1/2" funny pipes for connecting to these heads (as we ordinarily do for connecting other sprinker heads), or will I need to use larger pipes (say, 3/4" pipes) for connection purposes?

It would depend upon your designed flow rate of the Falcon head. The Falcon's specs indicate it supports flows ranging from about 3gpm to 21gpm.

Assuming funny pipe lengths are kept short, pressure losses shouldn't be a concern. The primary thing would be to avoid speeding. Plumbing standards call for a water "speed limit" of about 5fps (with 7fps being considered "reckless plumbing").

For flows below 5gpm, 1/2" should be ok.
For flows between 5-10gpm, 3/4" should be ok (10gpm pushing it).
If the flow exceeds 10gpm, 1" pipe would be required (and even that will exceed the speed limit if pushing the Falcon to its maximum flow of 20+gpm).

Because the Falcon is rated for flows upto 20+gpm, I understand why it has a 1" inlet.

On the subject of pressure losses, at the upper flow ranges I listed above, the pressure loss through just the funny-pipe would be about 1psi/10feet. So even in the 'worst' case, you only lose 1/2 psi if funny pipe is limited to 5'.

hookoo is that the case with funny pipe? i thought the psi loss would be more i posted this question along with another in the rotor section b/c using funny pipe is alot easier then hooking a riser right to the pipe....but i was worried about psi loss

If you're trying to replace a short riser with a little funny pipe (and we're talking inches and not feet), then pressure losses should be minimal through funny pipe.

As a guesstimate using friction loss charts for plastic pipe, it would seem that if you tried to force 20gpm through funny pipe (about equal to 1/2" pipe, perhaps a little smaller), your friction losses would be something on the order of 300 to 500 psi per 100'. So if your pipe is only 1 foot long, that's a 5psi pressure loss in the funny pipe IF your pushing 20gmp.

The bigger question would be do you want to try to force 20gpm through a 1/2" funny pipe. Because the speed of the water through the pipe would be HUGE, it would be better to use a larger pipe if you're trying to push that much water.

But unless this is a commercial install, I'm guessing your flow is going to be something closer to 10 gpm. At that rate, the pressure losses should be on the order of 80 to 200 psi per 100', so again, over a 1' distance, you'll only lose a few psi.

So the questions to then ask are #1, do you have a few psi to spare (or are you already pushing the design). #2, do you really want to push 10gpm through a 1/2" piece of funny pipe (because you'll be blowing the doors off that 5-7 ft/sec speed limit).

Can you find 3/4" funny pipe? If so and again you keep distances down to about 1', then pressure losses should be minimal and you might not be too bad on the speed limit issue (even at flows greater than 10gpm) just because the water is right at the sprinkler (i.e. the high flow at the tail of the pipe shouldn't cause water hammer).

Of course the other option would be swing arms, I know I've seen 3/4" material for that.